1. Field of the Invention
The present invention relates to an information processing apparatus that is capable of autonomously controlling supply of electric power inside the apparatus and a power control method for the information processing apparatus.
2. Description of the Related Art
In recent years, in the field of the computer system technology, power control techniques for reducing power consumption at standby time by stopping, supply of electric power inside an apparatus when processing is not performed and resuming the supply of electric power instantaneously when processing is required, for example, when input operation is applied to the apparatus have been developed.
For example, as a portable device such as a Personal Digital Assistant (PDA), there is known one that reduces power consumption at the standby time. When operation is not performed for a fixed time, the portable device automatically shifts to a low power consumption mode for operating a CPU at a low frequency and stopping supply of electric power to peripheral circuits and, when operation is performed, the CPU returns to an ordinary state to perform processing.
A general personal computer (PC) has functions such as a suspend mode and a standby mode. In particular, in a battery-driven device such as a notebook PC, the suspend mode or the standby mode is effective for reduction of unnecessary power consumption at the time when the PC is not used for a long time.
Note that a technique concerning power control such as the suspend mode and the standby mode is disclosed in JP9-114557A.
However, in the conventional power control technique, as a premise, electric power is supplied to a CPU and other functional units (a display, a memory, etc.) in a normal state of use. Power consumption is reduced only under a specific condition, for example, when a fixed time elapses from immediately preceding operation.
Therefore, usually, regardless of the fact that some of the units are not operating in an apparatus, electric power is supplied to the respective units until the specific condition is met, for example, until the fixed time elapses from immediately preceding operation. This causes unnecessary power consumption.
For example, when it is evident that the apparatus is operated by a user intermittently, more specifically, in an apparatus in which, as a premise, an electronic book is inspected and operation for turning a page is performed at certain time intervals, unnecessary electric power is supplied to some units, which are not operating, among units of the apparatus until a fixed time elapses after the operation for turning a page.
On the other hand, in order to reduce unnecessary power consumption, it is conceivable to use the standby mode or the suspend mode.
However, in recent years, shrinkage of a semiconductor process has been in progress, which causes an increase in a leak current. In the standby mode, power consumption due to a leak current of a CPU is innegligible at the standby time when an apparatus is put in a HALT state.
In addition, in the suspend mode, since a fixed time is required for returning to an operation mode. Thus, operation performed by a user cannot be executed promptly.